There were large velocity warnings during processing therefore the ambiguity velocity was increased on station 4 to 3 m s -1 , on station 11 to 3.5 m s -1 and on station 20 to 4.0 m s -1 .

In an attempt to increase sampling the pinging interval was decreased to 1.0/1.3 s on station 20. Inspection of the raw ensemble times indicated that the instruments were not capable of such a high pinging rate and the rate was therefore decreased to 1.2/1.4 s on station 23 and, finally, to 1.3/1.5 s on station 33.

Due to a problem with the star cable, station 41 was carried out with asynchronous pinging, with a staggered rate of 1.3/1.5 s in the master and 1.0 s in the slave.

There are no uplooker data for station 39 because of cable problems, and no valid uplooker data for station 54 due to hardware problems.

BODC Processing

LDEO processed data were provided by the originator in Matlab and ASCII formats. The LDEO processed data in ASCII format were converted into BODC internal format after discussion with the originator. All data provided were from the downward looking RDI 300 kHz Workhorse ADCP which was in operation at the time. The following table shows how the variables within the ASCII files were mapped to appropriate BODC parameter codes:

Originator's Parameter Name

Units

Description

BODC Parameter Code

Units

Comments

z

m

Depth of LADCP bin

ADEPZZ01

m

-

u

m s -1

Eastward velocity

LCEWLW01

cm s -1

Units converted from m s -1 to cm s -1 by multiplying by 100.

v

m s -1

Northward velocity

LCNSLW01

cm s -1

Units converted from m s -1 to cm s -1 by multiplying by 100.

ev

m s -1

Uncertainty estimates of LADCP velocity profile

ERRVLDCP

cm s -1

Units converted from m s -1 to cm s -1 by multiplying by 100.

All reformatted data were visualised using the in-house Edserplo software. Suspect and missing data were marked by adding an appropriate quality control flag.

Note that the more complex LDEO processed data are available on request in Matlab format as well as the unprocessed raw LADCP files.

Originator's Data Processing

Sampling Strategy

A total of 55 LADCP profiles were collected at all CTD stations in order to derive full-depth profiles of ocean velocity, as well as profiles of finestructure vertical shear.

Data processing

Preliminary shipboard processing of the LADCP data was carried out with the LDEO IX.6 LADCP processing software using one second averaged uncalibrated CTD data in order to correct the LADCP data for depth and sound speed. The CTD data were minimally processed using 'AlignCTD' which applies temporal shifts to align the sensor readings and 'CellTM' which corrects for the thermal mass. Velocity referencing was accomplished with post-processed (i.e. non-RDI) bottom-track data, 75kHz VMADCP data, and GPS information in the CTD time series files. The first bin of each instrument was discarded during processing. Note that the profiles 2, 23, 26, 35, 45, 47, 50, 52, 53 and 55 were not processed with bottom tracking and profile 7 did not have bottom tracking or VMADCP data.

Please refer to Thurnherr (2014) and cruise report for a more detailed processing methodology. However, please be aware that this processing guide is for software versions IX.7 to IX.10 only, and changes have been made between versions which have the potential for significantly changing the solutions.

DIMES is a US/UK field program aimed at measuring diapycnal and isopycnal mixing in the Southern Ocean, along the tilting isopycnals of the Antarctic Circumpolar Current.

The Meridional Overturning Circulation (MOC) of the ocean is a critical regulator of the Earth's climate processes. Climate models are highly sensitive to the representation of mixing processes in the southern limb of the MOC, within the Southern Ocean, although the lack of extensive in situ observations of Southern Ocean mixing processes has made evaluation of mixing somewhat difficult. Theories and models of the Southern Ocean circulation have been built on the premise of adiabatic flow in the ocean interior, with diabatic processes confined to the upper-ocean mixed layer. Interior diapycnal mixing has often been assumed to be small, but a few recent studies have suggested that diapycnal mixing might be large in some locations, particularly over rough bathymetry. Depending on its extent, this interior diapycnal mixing could significantly affect the overall energetics and property balances for the Southern Ocean and in turn for the global ocean. The goals of DIMES are to obtain measurements that will help us quantify both along-isopycnal eddy-driven mixing and cross-isopycnal interior mixing.

Fixed Station Information

Station Name

Drake Passage

Category

Offshore area

Latitude

59° 0.00' S

Longitude

62° 0.00' W

Water depth below MSL

Drake Passage

The World Ocean Circulation Experiment (WOCE, 1990-1998) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.

The Drake Passage is the narrowest constriction of the Antarctic Circumpolar Current (ACC) - the largest current in the world and connects all three major oceanic basins both horizontally and vertically, thus being a key control in the global overturning circulation.Within the Drake Passage, two repeat hydrographic sections (SR1 and SR1b) were established by WOCE. These were designed to extend measurements collected earlier by the International Southern Ocean Studies (ISOS) programme and have continued beyond the WOCE time-frame.

The original section was SR1 (which also covers part of the A21 one time survey track). Subsequently, the section was shifted to the east (and designated SR1b) in order for it to lie on a satellite ground track as illustrated in the image below.

In addition to the hydrographic measurements, UK research in Drake Passage also includes a network of coastal and deep tide gauges, analysis of satellite altimeter data, and state-of-the-art global numerical modeling.